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engine are being subjected to intense friction, is it not reasonable to assume that the same amount would be sufficient for different rates of speed? Upon what hypothesis can it be assumed that one-thirty-second of an inch is sufficient opening at a moderate rate of speed and that three-eighths of an inch is necessary at a higher speed ?”.
Exactly; and if a small amount of lead is demanded by those who think it necessary at certain times, the use of the Walschaert gear will prevent that amount from increasing as the speed increases and the reverse lever is hooked up.
One night the writer was firing a little 4-4-0, 17-inch by 24-inch engine pulling a very heavy passenger train, when we broke down and had to disconnect the engine on one side. After fixing things up in good shape we proceeded; there was only one more stop to be made short of our journey's end, but in spite of the efforts of the engineer, we came to a standstill at that station with the working engine on an exact dead centre.
It was decided to unlock the Janney coupler behind the tender, leaving the safety chains coupled, and "pinch” the engine ahead and off the dead centre, and with the Janney set to couple, to pull the train a few feet by the safety chains and allow the coupling to “make”--trusting to luck to stop again with the
crank-pin off the centre, in order to re-couple the air hose.
The trainmen took turns operating the pinch-bar, but their efforts were in vain. I noticed, however, that just before their groans began to indicate the application of cause toward hoped-for effect, the engineer had opened the throttle-valve pretty strong. The engine would not move, however, and the engineer finally shut off steam, jumped down from the engine and took the bar: “Now, Billy! Give 'er steamhere she goes!” he promised; but she wouldn't move; he kept on trying, with no better results, so I shut off steam and opened the cylinder cocks.
The conductor had about decided to send for the section men, when the engineer concluded to try the pinch-bar again, and calling to me to open the throttle, he threw himself at it once more: “Lay on, Macduff!” thought I, with a sudden idea, and I did not open the throttle valve this time; the result was that the engine responded to the pinch-bar as promptly, and was kept moving with as much ease as if it were an empty flatcar.
That night, then and there, I lost all of my confidence in the theory of lead. It was proven that lead not only fails to be of any assistance in carrying an engine past the dead centre but offers resistance to the crank-pin's movement past the dead point. The force that lead
causes to be exerted when the engine is on a dead centre absorbs, or nullifies, much of the energy furnished by the other source of power at its zenith-the engine on the other side, with its admission port wide open and the relation of crank-pin to driving-axle giving the maximum leverage.
If the pre-admission of steam to the cylinder, that is referred to as lead, is finally conceded as necessary only for cushioning the piston at the completion of its stroke, any argument for it is now clearly fallacious, for the reason that the exhaust may be cut off at any point toward the finish of the piston's stroke and the resultant compression will produce the cushioning effect just as well—and more economically,—as evidenced by the quoted authority, than by means of any
pre-normal opening of the admission port. • Motive-power officials often try to induce engineers to run their engines with full open throttle and reverse lever hooked up to the limit, claiming that an engine would run faster and work more economically that way. That method has been tried, fairly, and also the other one of using a lighter throttle and a little longer travel of the valves, and invariably the latter way gave the best results, both in speed and fuel economy. It is not imagination, and might be attributed to the fact that the lower down the link is worked the less the lead, with the Stephenson motion, and the
less “friction on the bearings of the rods and crankpins” there will be. Of course, it may be said in answer, that there is but a slight increase in the amount of lead from the point where the engineer worked the lever up to the point at which the master mechanic wanted it worked; yet there was a difference, and an otherwise unexplained variance in the performances of the engine-favorable to the position of the reverse lever in which it is claimed by some that the steam is “wire-drawn."
The simplest test to prove the superiority of the Walschaert valve gear, and the easiest to makc, yet most convincing to the practical mind, is, where there are engines of the same general type except that some are equipped with the Stephenson link and others have the Walschaert gear, to note the boiler pressure required to move each of these engines from its stall in the roundhouse, with its cylinders “cold.” The test with big “battleship” engines has shown that eighty-five pounds on the steam gauge were required to get the engine with the old link motion on the turntable, while the engine having the Walschaert valve gear was moved out, easily, with the gauge showing thirty-five pounds of steam.